1. Field of the Invention
The present invention relates to a vehicle seat and, more particularly, to a vehicle seat which incorporates air bags therein so as to provide support portions of a predetermined form on the surface of the vehicle seat.
2. Description of the Prior Art
Conventionally, there have been proposed and practiced some vehicle seats in which air bags are employed instead of mechanical adjustment means in support sections including thigh support sections and side support sections in a seat cushion as well as lumbar support sections and side support sections in a seat back to variably adjust their forms or sitting pressures. Such air bags can be expanded or contracted by means of feed-in or discharge of air so as to adjust the forms and sitting pressures of these support sections, respectively.
Examples of the conventional seats of this type in which air bags are included are those shown in FIGS. 1, 2 and 3.
Specifically, FIG. 1 illustrates a centrally longitudinal section view of a seat back forming a part of an example of the conventional seats provided with air bags therein, and FIG. 2 shows a transverse cross section view taken along line I--I in FIG. 1. As shown in these figures, in this seat back (1) there are provided air bags (4) and (5) between a seat pad (6) and a top member (7) such that they are located at a lumbar support section (2) and at side support sections (3)(3), respectively.
With such structure, however, when air is fed into the air bags (4) and (5) so as to expand them and thus operate the support sections (2) and (3),(3), actually, the support sections (2) and (3)(3) can not be expanded outwardly so much. This is because the expansion of the air bags (4) and (5) is restricted by the general tension force of the top member (7) extended over the seat so that the seat pad (6) between a seat frame (8) and the air bags (4)(5) is compressed. Such structure also presents another problem. Since the expansion forces of the air bags (4) and (5) are applied directly to the top member (7), respective support sections (2) and (3)(3) are locally expanded and the air pressure is applied via the top member (7) directly to an occupant of the seat so that the occupant may be given a strange feeling.
Next, another example of the prior art seat of this type is described with reference to FIG. 3, which is similar to FIG. 1, that is, a longitudinally sectional side view of a seat back portion of the seat. In FIG. 3, reference (9) designates an air bag.
The air bag (9) of this prior art seat, as shown in FIG. 1, is mounted onto the surface of a top member (7). In this case, since the expansion force of the air bag (9) is directed directly to the occupant when it is expanded, its extension effects due to its expansion may not be reduced as in the conventional seat in FIG. 1, but the air bag (9) will give the occupant a substantially greater stange feeling. The reason why such greater strange feeling is produced is the fact that since the air bag (9) is in direct contact with the occupant it is expanded toward its portions where a smaller sitting pressure is applied between the occupant's back and the seat back so that its remaining portions suffering from a larger sitting pressure are given away, that is, the air bag (9) is not expanded little at its portions where supporting is most needed or the highest sitting pressure is applied so that it is extended out at its portions where no supporting effects are required only. In addition, since the occupant is sitting via the air bag against the seat back during running of the vehicle, the occupant may be easily vibrated by means of the air pressure of the air bag when the vehicle is vibrated, which makes the occupant unstable and uncomfortable during sitting.